1. Field
This disclosure relates to testing a communications network and specifically to verify that a video path exists between two devices connected to the network.
2. Description of the Related Art
Traditionally, video images were transmitted from a central location to video receivers via wireless broadcasting or though primarily unidirectional communications networks such as cable television distribution systems. However non-traditional video-capable communications devices have proliferated in recent years. Devices such as personal computers, e-mail appliances, web appliances, and cellular telephones are capable of receiving and displaying video images. In many cases, these devices are also capable of capturing and transmitting video images.
With the exception of analog public broadcasting and cable TV systems, video images are typically transmitted over a network in the form of digital packets. The video signal is first coded using an algorithm that compresses the bandwidth of the signal. The coded video signal is then encapsulated in packets, each of which contains a portion of the original signal. The packets are then routed through the network to a destination device. Upon receipt at the destination device, the packets are reassembled and decoded to reconstruct the video signal.
The transmission of video information through a network is more complex than the transmission of simpler digital information. The existence of a path between two devices for e-mail or text messages may not confirm the existence of a video path between the same two devices. For example, a video path may not exist because of incompatibility between the coder at the transmitting device and the decoder at the receiving device. In addition, the transmission of video information can be degraded or precluded by excessive numbers of damaged, lost, or out-of-sequence packets.
Throughout this description, elements appearing in block diagrams are assigned three-digit reference designators, where the most significant digit is the figure number and the two least significant digits are specific to the element. An element that is not described in conjunction with a block diagram may be presumed to have the same characteristics and function as a previously-described element having a reference designator with the same least significant digits.